- Unable or unwilling to discontinue use of inducers and inhibitors of CYP450 listed in Appendix 13.4 and BCRP and PgP inducers and inhibitors for at least 14 days or five half-lives of a drug (whichever is longer) prior to the first dose of study drug and for the duration of the study. (CYP3A4 substrates can be administered, but investigators will need to be aware of possible increased or decreased effectiveness of the non-study drug and this should be recorded in concomitant medications. Dexamethasone is acceptable although listed as a CYP3A4 inducers/inhibitors as long as the dose is 16 mg/day or lesser.